1. Field of the Invention
The present invention relates to filling machines of a conditioning plant and more particularly to a method and a device for sequentially selecting and weighing containers which have been filled on a filling machine and for selectively establishing a correlation with the respective filling stations of the machine for eventually correcting the amounts of material delivered into the containers in said filling machine.
The present invention also relates to a method for sequentially selecting the filled containers, for controlling the amount of material delivered into the containers and for correcting the weight of material to be delivered at the respective filling stations of the filling machine with respect to a reference value.
The present invention relates more particularly, but not exclusively, to rotative weighing filling machines.
Multi-station rotative filling machines of the weighing type generally comprise a rotating assembly including a hopper or a tank for the material to be filled, a plurality of filling heads, and weighing metering stations disposed below said filling heads and functionally connected thereto.
In operation, the containers to be filled are continuously fed to the respective weighing stations where they control the opening of the filling heads whereby, when the required amount, e.g. weight, of material has been delivered from the tank into the containers, the weighing control device of each weighing metering station generates a signal for shutting the corresponding filling head. The filled container is thus forwarded toward a shutting or sealing machine.
The weight of the material dispensed within a container must be legally within a given range around a predetermined value and it is essential that storage conditioning will be permanently made with machines fullfilling said legal requirements.
2. Description of the Prior Art
Weight control is generally normally performed as follows:
selecting at the outlet of the filling machine a number of successive filled containers equal to the number of the stations in the machine and establishing a correlation between said series of containers and the filling stations of the machine where they have been filled;
weighing on an external check-weigher said selected filled containers;
eventually repeating later said operations;
determining and plotting the weight standard deviation with respect to the authorised range; and
adding or withdrawing calibrated weights on the faulty weighing metering stations for adjustment of the stations which deliver an amount of material beyond the authorized range.
Said manual operations as a whole are easy to be carried on, do not imply the machine to be stopped and only require localized external intervening, i.e. adding or withdrawing calibrated weights.
However, when it is required to package with such a machine materials of different nature or when the capacity or the form of the containers to be filled vary in a same packaging line, said control operative steps has to be effected for each of said modifications.
Moreover, with usual minimum rates of productions, for instance of about 7,000 one-liter containers per hours, more than 100 containers leave the filling machine each minute, i.e. about two containers per second. If the packaging rate is doubled or tripled, as it is usually required nowadays, or if the containers are smaller (for instance half-liter containers) and thus more quickly filled, the delivery rate of filled containers is such that the operator has difficulties in doing the control steps, as above described.
If there are combined problems in production rate and of packaging modifications in a same packaging line, the control becomes excessively time-spending and critical, whereby increasing the risks of errors and operating costs of said machine.
It has been accordingly found desirable to provide a filling machine of the above described type with means capable of:
(a) automatically carrying out a comparison weighing of the containers which have been filled on each filling station;
(b) indicating the measured deviation, if any;
(c) directly acting on each related filling station for which a deviation has been established; and
(d) repeating control weighing after adjustment for controlling said adjustment.
A typical multi-station weight controlled filling machine to which the present invention may be applied is disclosed in French Pat. No. 2,168,696 which is incorporated here for reference.